The fuel cell is expected to be a future energy-generation apparatus because the fuel cell has high energy conversion efficiency, is clean, and produces very little noise. Fuel cells have recently been used not only as automotive and residential power generators, but have also been installed into small electrical equipments such as mobile phones, notebook personal computers, and digital cameras because of their high energy density to possibly operate for a longer period of time than a conventional secondary battery, and have been attracting attention. However, further cost reduction is required for a fuel cell used as an automotive or residential power generator, and the amount of catalysts uses is desirably reduced as a way for cost reduction. Practical application of a fuel cell as a generator for small electrical equipments requires the size reduction of an entire system and the improvement of power generation efficiency.
Hitherto, an attempt has been made at forming a catalyst into fine particles and carrying the catalyst on carbon particles or the like to attain three-dimensional dispersion, to thereby increase the surface area and improve the catalyst utilization efficiency. Meanwhile, another attempt has been made at forming a catalyst layer into a very small thickness of about several μm, to thereby facilitate the substance transport. Further, a catalyst layer was gathered in the vicinity of a polymer electrolyte membrane, to thereby increase an effective surface area of the catalyst. Particularly when a fuel cell is to be installed in a small-sized electric equipment, the fuel cell itself needs to be small in size, and air is often supplied to an air electrode from air holes through natural diffusion (air breathing system) without use of a pump or a blower. In this case, substance transport at the air electrode often becomes a reaction rate-determining factor, and the thickness reduction of a catalyst layer seems to be effective means. In contrast to this, a vapor phase method such as sputtering is effectively used as means for forming a thin film and a method of producing a thin film catalyst layer having a large specific surface area and high activity by sputtering is disclosed in Japanese Patent Application Laid-Open No. 2006-49278.